Microfluidic autoregulator devices are shown in US Pat. App. No. 2007/0119510 A1 as mentioned above. For the sake of clarity and ease of read, some aspects of that disclosure are summarized in this section.
FIG. 1 shows a top view of a current source (100). Fluid flows from an origin (110) to a sink (120) along a flow channel (130). The current source (100) is referenced as a “detour” current source in view of a dead-end detour (145) provided from a detour split (135) into a detour channel (140) and through a via (150) ending at a valve (160). It is noted from FIG. 1 that the valve (160) is located in a different plane than the rest of the current source (100), i.e. then the remaining part of the current source (100) which includes sections indicated by reference numbers (110), (120), (130), (135), (140). A connection between the valve (160) and the rest of the current source (100) is made through the via (150). The valve (160) has a function of controlling the throughput of the current source (100).
When viscous laminar flow is established into the flow channel (130), e.g. by applying pressure at the origin (110) and allowing the fluid to leave at the sink (120), Poiseuille's law establishes that static pressure will decrease from the origin (110) to the sink (120) down the flow channel (130). Simultaneously, there is no flow in the dead-end detour channel (140), so a static pressure there is constant and the same as the one at the detour split (135). As a result, a pressure difference is generated across the valve (160) and therefore the valve (160) constricts the flow channel (130). Thus an overall fluidic resistance of the flow channel (130) increases with applied pressure between the origin (110) and the sink (120). The result is a non-linear device.
FIG. 2 shows a current source (200) in a “loop” configuration. Differently from the embodiment of FIG. 1, the current source (200) is not using a detour. The flow channel (230) passes through a valve (260), forming a loop (235) to the sink (220) through a via (250) and a channel (240). It is noted from FIG. 2 that the channel (240) and the sink (220) are located in a separate plane from that of the rest of the current source (200), i.e from that of the remaining part of the current source (200) which includes sections indicated by reference numbers (210), (230), (260).
In a similar way as described above in reference to FIG. 1, when fluid flows into the current source (200) by applying a pressure at an origin (210), a pressure difference across the valve (260) based on the Poiseuille's law results in a channel constriction. Hence, overall device resistance to flow from the origin (210) to the sink (220) increases as applied pressure increases resulting in a non-linear behavior of the current source (200).
Referring to the representation of FIG. 1, the current source (100) comprises a multi-layer chip (not shown in this view) and can be constructed in two different configurations, “pushdown” (in which the valve (160) is fabricated above the main channel (130) and a valve membrane (not shown in this view) deflects downward to constrict the main channel (130)), or “pushup” (in which the valve (160) is fabricated below the main channel (130) and the valve membrane deflects upward to constrict the main channel (130)). In the same way, referring to FIG. 2, a relative position of valve (260) and main channel (240) determines and allows for “pushdown” and “pushup” configurations to be executed with the loop current source (200). Therefore, four types of autoregulatory architectures are possible: pushdown detour, pushup detour, pushdown loop, and pushup loop.
Further referring to FIG. 1, by varying various dimensions the current source (100), throughput can be controlled. As an example, by changing a detour ratio L1/L, the current source (100) throughput saturation level can be modified. As another example, varying the valve width W results in different throughput saturation levels. The larger the valve width W, the lower the throughput saturation level, while lowering saturation is important in building autoregulators of superior performance and quality. However, increasing the valve (160) width while maintaining the same thickness of membrane results in a flabby structure which may cause manufacturing issues. As an example, a flabby membrane can sag downward by gravity and get stuck in a lower channel during fabrication. This defect is usually irreversible in view of the material curing during a manufacturing process. Such effects pose challenges in manufacturing current sources with lower saturation points.